Pivotal bone anchor receiver assembly with unitary and multi-part interchangeable threaded closures

ABSTRACT

A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a head and a closed retainer ring. The external capture structure surface and retainer ring internal bore surface are both threaded for rotatable attachment within a cavity of the head. The head has a U-shaped cradle defining a channel for receiving a spinal fixation rod. The head channel communicates with the cavity and further with a restrictive opening that allows for loading the capture structure into the head but prevents passage of the closed retainer ring out of the head. The retainer ring has an external substantially spherical surface that mates with an internal surface of the head, providing a ball joint, enabling the head to be disposed at an angle relative to the shank body. The threaded capture structure or the closed retainer structure includes a tool engagement formation and gripping surfaces for non-slip engagement by a tool for driving the shank body into bone.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/612,906, filed Feb. 3, 2015, which is a continuation of U.S.patent application Ser. No. 13/896,490, filed May 17, 2013, now U.S.Pat. No. 8,998,960, which is a continuation of U.S. patent applicationSer. No. 12/807,937, filed Sep. 17, 2010, now U.S. Pat. No. 8,444,677,which is a continuation of U.S. patent application Ser. No. 10/986,377,filed Nov. 10, 2004, now U.S. Pat. No. 7,833,250, each of which is fullyincorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

The present invention is directed to polyaxial bone screws for use inbone surgery, particularly spinal surgery. Such screws have a head thatcan swivel about a shank of the bone screw, allowing the head to bepositioned in any of a number of angular configurations relative to theshank.

Many spinal surgery procedures require securing various implants to boneand especially to vertebrae along the spine. For example, elongate rodsare often utilized that extend along the spine to provide support tovertebrae that have been damaged or weakened due to injury or disease.Such rods must be supported by certain vertebrae and support othervertebrae.

The most common mechanism for providing vertebral support is to implantbone screws into certain bones which then in turn support the rod or aresupported by the rod. Bone screws of this type may have a fixed headrelative to a shank thereof. In the fixed bone screws, the head cannotbe moved relative to the shank and the rod must be favorably positionedin order for it to be placed within the head. This is sometimes verydifficult or impossible to do. Therefore, polyaxial bone screws arecommonly preferred.

Polyaxial bone screws allow rotation of the head about the shank until adesired rotational position of the head is achieved relative to theshank. Thereafter, a rod can be inserted into the head and eventuallythe head is locked or fixed in a particular position relative to theshank.

A variety of polyaxial or swivel-head bone screw assemblies areavailable. One type of bone screw assembly includes an open head thatallows for placement of a rod within the head. A closure top or plug isthen used to capture the rod in the head of the screw.

Because such implants are for placement within the human body, it isdesirable for the implant to have as little effect on the body aspossible. Consequently, heavy, bulky implants are undesirable andlighter implants with a relatively small profile both in height andwidth are more desirable. However, a drawback to smaller, lighterimplants is that they may be more difficult to rigidly fix to each otherand into a desired position. Lack of bulk may also mean lack ofstrength, resulting in slippage under high loading. Also, more componentparts may be required to rigidly fix the implant in a desired position.A further drawback of smaller components is that they may be difficultto handle during surgery because of their small size, failing to provideadequate driving or gripping surfaces for tools used to drive the shankinto bone.

One undesirable attribute of some of the swivel-head implants is theneed for a multitude of components that may loosen or even disassemblewithin the body. It is most undesirable for components to be free tomove around in the body after the completion of surgery. Loosening ofcomponents relative to each other may result in related undesirablemovement of the bone or vertebra that the implant was intended tostabilize.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more of the problemsdescribed above. Further objects of the invention include: providing apolyaxial bone screw with features that provide adequate frictional orgripping surfaces for bone implantation tools and may be readily,securely fastened to each other and to bone. Also, if the implant shouldslip or become loose for some reason, an object of the invention is toprovide an implant wherein all of the parts remain together and do notseparate. Furthermore, it is an object of the invention to provide alightweight, low profile polyaxial bone screw that assembles in such amanner that the components cooperate to create an overall structure thatprevents unintentional disassembly.

A polyaxial bone screw assembly of the present invention includes ashank having a body for fixation to a bone. Integral with the shank andextending axially upwardly and outwardly therefrom is a capturestructure. The capture structure has a radially projecting outer surfacethat is substantially cylindrical and that further includes a helicallywound structure, such as a thread. The upper end of the shank isconvexly curved.

The bone screw assembly further includes a head having a top portion anda base. The top portion is open and has a channel. The base also isupwardly open and includes an inner seating surface partially defining acavity and has a lower aperture or opening. The channel of the topportion communicates with the cavity, which in turn communicates with anexterior of the base of the head through the base opening. The baseopening is sized and shaped to receive the capture structure of theshank into the head cavity.

The bone screw assembly also includes an integral one piece contiguouslyclosed ring-like retainer structure that has an internal surface with ahelically wound structure thereon, such as a thread. The thread of theretainer structure is sized and shaped to mate with the thread of theshank capture structure when the retainer structure and the capturestructure are coaxially aligned within the head cavity, thereby securingthe retainer structure to the capture structure.

The external surface of the retainer structure is configured to be inslidable mating engagement with the surface defining the cavity of thehead. Preferably, the retainer structure external surface and the matinghead inner surface are substantially spherical. However, it is notedthat the mating surfaces may be of another shape, such as conical ortapered, especially for the head cavity inner surface. The cooperatingshapes of the retainer external surface and the head inner surfaceenable selective angular positioning of the shank body with respect tothe head.

In one embodiment according to the invention, the capture structureincludes a tool engagement formation that extends or projects from thecapture structure and is located between the curved upper end and thethreaded cylindrical portion thereof. In another embodiment of theinvention, the closed ring-like retainer structure includes a toolengagement formation. In both embodiments, the tool formation is fornon-slip engagement by a tool for driving the shank into bone and mayalso be cooperatively used for attaching the retainer structure to thecapture structure.

Also according to the invention are tool seating surfaces that may bedisposed on one or both of the capture structure and the retainerstructure. In one embodiment, the shank capture structure includes toolengagement surfaces that are positioned and shaped to receive a sockettype tool and a planar, tool seating surface extending radially from thelower end of the tool engagement surfaces. The seating surface isdisposed coaxially with the shank body. The retainer structure hasmating seating surfaces that cooperate with the shank capture structureseating surface. The tool seating surfaces and the tool engagementsurfaces partially define a recess for receiving a driving tool matingwith the tool engagement surfaces. When engaged, the driving tool is incontact with the capture structure tool seating surface, providinggreater mating surface to the capture structure tool engagement surfacesso as to provide additional surface for frictional gripping when theshank body is driven into bone, especially harder bone.

In certain embodiments a tool seating and partially surrounding surfacemay be disposed on the retainer structure according to the inventionsuch that when the retainer structure is mated with the capturestructure, the retainer structure seating surface extends radially fromthe lower end of the tool engagement surfaces and is disposed coaxiallywith respect to the shank body.

In certain embodiments, both the capture structure and the retainerstructure may include tool seating surfaces that extend radially in thesame plane when the capture structure and the retainer structure aremated. In such embodiments, the two tool seating surfaces and the shanktool engagement surfaces partially define a recess for receiving adriving tool engaged with the tool engagement surfaces. When engaged,the driving tool is in contact with both tool seating surfaces, therebyseating the tool lower relative to the tool engagement surfaces andproviding additional frictional gripping surface when the shank body isdriven into bone.

A polyaxial bone screw assembly method according to the inventionincludes inserting an independent closed ring-like retainer into a headcavity, inserting a capture structure of a bone screw shank through ashank receiving opening of the head and into a cavity thereof; andattaching the capture structure to the retainer structure within thehead.

A method according to the invention further includes driving the shankbody into bone by rotating the shank body with a tool engaged with atool engagement formation, such as a pair of aligned and spaced slots,disposed on the capture structure or the retainer structure. Furtherassembly steps according to the invention include inserting a rod intothe channel; and biasing the rod against a top of the bone screw shankcapture structure by rotatably inserting a closure member structurewithin or onto a mating structure of the rod receiving channelstructure.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

Other objects and advantages of this invention will be apparent to thoseskilled in the art from the following description taken in conjunctionwith the drawings and the appended claims.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a polyaxial bone screwassembly according to the present invention having a shank with acapture structure at one end thereof, a head, and a closed ring-likeretainer structure and further showing a rod and closure structure.

FIG. 2 is an enlarged top plan view of the retainer structure of FIG. 1.

FIG. 3 is an enlarged cross-sectional view of the retainer structure ofFIG. 2, taken along line 3-3 of FIG. 2.

FIG. 4 is an enlarged top plan view of the shank of FIG. 1.

FIG. 5 is an enlarged cross-sectional view of the shank, taken alongline 5-5 of FIG. 4.

FIG. 6 is an enlarged cross-sectional view of the head, taken along theline 6-6 of FIG. 1, and showing the retainer structure seated in thehead (in solid lines) and illustrating the retainer structure beinginserted into the head (in dashed lines).

FIG. 7 is an enlarged cross-sectional view of the head and retainerstructure similar to FIG. 6, showing the shank capture structurepartially threaded into the retainer structure.

FIG. 8 is an enlarged cross-sectional view of the head and retainerstructure similar to FIG. 7, illustrating the fully assembled shank andretainer structure pivoted to a selected angle relative to the head.

FIG. 9 is an enlarged cross-sectional view of a vertebra, and head andretainer similar to FIG. 7, showing the shank being implanted into thevertebra using a driving tool mounted on the shank capture structure.

FIG. 10 is an enlarged, fragmentary cross-sectional view of the head,rod and vertebra, similar to FIG. 8 and further showing the closuremember structure in contact with the rod and the rod in contact with thecapture structure.

FIG. 11 is a fragmentary and enlarged perspective view of the assemblyof FIG. 1 shown completely assembled.

FIG. 12 is an exploded perspective view of an alternative embodiment ofa polyaxial bone screw assembly according to the present inventionhaving a shank with an upper capture structure, a head, and a closedring-like retainer structure.

FIG. 13 is an enlarged top plan view of the retainer structure of FIG.12.

FIG. 14 is an enlarged cross-sectional view of the retainer structure ofFIG. 13, taken along line 14-14 of FIG. 13.

FIG. 15 is an enlarged top plan view of the shank of FIG. 12.

FIG. 16 is an enlarged cross-sectional view of the shank of FIG. 12,taken along line 16-16 of FIG. 15.

FIG. 17 is an enlarged cross-sectional view of the head of FIG. 12showing the retainer structure seated in the head, taken along line17-17 of FIG. 12.

FIG. 18 is an enlarged cross-sectional view of the head and retainerstructure similar to FIG. 17, showing the shank capture structurepartially assembled with respect to the retainer structure.

FIG. 19 is an enlarged cross-sectional view of the head and retainerstructure, similar to FIG. 18, illustrating the shank and retainerstructure being pivotable to selected angles relative to the head insolid and phantom lines.

FIG. 20 is an enlarged and fragmentary perspective view, similar to FIG.19, illustrating the use of a punch tool to lock the position of theretainer structure relative to the capture structure.

FIG. 21 is an enlarged and partial view similar to FIG. 20 showing athread of the capture structure deformed to rigidly secure the retainerstructure to the capture structure.

FIG. 22 is an enlarged cross-sectional view of a vertebra, and the headand retainer structure of FIG. 12, showing the shank being implantedinto the vertebra using a driving tool mounted on the shank capturestructure and the retainer structure.

FIG. 23 is an exploded fragmentary, partially cross-sectional view ofthe embodiment of FIG. 12, showing a rod in contact with the domed upperextension of the capture structure and illustrating a two-piece closuremember structure and driving tool for biasing the rod against the domedupper extension of the capture structure.

FIG. 24 is an enlarged cross-sectional view of the assembly of FIG. 23shown completely assembled.

FIG. 25 is an enlarged perspective view of the assembly of FIG. 23 showncompletely assembled.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

In FIGS. 1-11 the reference number 1 generally represents a firstembodiment of a polyaxial bone screw apparatus or assembly according tothe present invention. The assembly 1 includes a shank 4 that furtherincludes a body 6 integral with an upwardly extending capture structure8; a head 10; and a closed integral retainer structure or ring 12. Theshank 4, head 10 and retainer structure 12 preferably are assembledprior to implantation of the shank body 6 into a vertebra 15, whichprocedure is shown in FIG. 9.

FIG. 1 further shows a closure structure 18 of the invention for biasinga longitudinal member such as a rod 21 against the capture structure 8which biases the ring 12 into fixed frictional contact with the head 10,so as to fix the rod 21 relative to the vertebra 15. The head 10 andshank 4 cooperate in such a manner that the head 10 and shank 4 can besecured at any of a plurality of angles, articulations or rotationalalignments relative to one another and within a selected range of anglesboth from side to side and from front to rear, to enable flexible orarticulated engagement of the head 10 with the shank 4 until both arelocked or fixed relative to each other near the end of an implantationprocedure.

The shank 4, best illustrated in FIGS. 1 and 5, is elongate, with theshank body 6 having a helically wound bone implantable thread 24extending from near a neck 26 located adjacent to the capture structure8 to a tip 28 of the body 6 and extending radially outward therefrom.During use, the body 6 utilizing the thread 24 for gripping andadvancement is implanted into the vertebra 15 leading with the tip 28and driven down into the vertebra 15 with an installation or drivingtool 31, so as to be implanted in the vertebra 15 to near the neck 26,as shown in FIG. 9, and as is described more fully in the paragraphsbelow. The shank 4 has an elongate axis of rotation generally identifiedby the reference letter A. It is noted that any reference to the wordstop, bottom, up and down, and the like, in this application refers tothe alignment shown in the various drawings, as well as the normalconnotations applied to such devices, and is not intended to restrictpositioning of the assembly 1 in actual use.

The neck 26 extends axially outward and upward from the shank body 6.The neck 26 is of reduced radius as compared to an adjacent top 32 ofthe body 6. Further extending axially and outwardly from the neck 26 isthe capture structure 8 that provides a connective or capture apparatusdisposed at a distance from the body top 32 and thus at a distance fromthe vertebra 15 when the body 6 is implanted in the vertebra 15.

The capture structure 8 is configured for connecting the shank 4 to thehead 10 and capturing the shank 4 in the head 10. The capture structure8 has an outer substantially cylindrical surface 34 having a helicallywound advancement structure thereon which in the illustrated embodimentis a V-shaped thread 36 disposed adjacent to a seating surface 38 andextending to a location near a rim 37. The rim 37 is adjacent to theneck 26. Although a simple thread 36 is shown in the drawings, it isforeseen that other structures including other types of threads, such asbuttress and reverse angle threads, and non threads, such as helicallywound flanges with interlocking surfaces, may be alternatively used inalternative embodiments of the present invention. The cylindricalsurface 34 could be truncated giving a non-contiguous helically woundstructure.

The shank 4 further includes a tool engagement structure 40 disposednear a top end surface 42 thereof for engagement of the driving tool 31shown in FIG. 9 which includes a driving structure in the form of asocket. The tool 31 is configured to fit about the tool engagementstructure 40 so as to form a socket and mating projection for bothdriving and rotating the shank body 6 into the vertebra 15. Specificallyin the embodiment shown in FIGS. 1-11, the tool engagement structure 40is in the shape of a hexagonally shaped extension head coaxial with boththe threaded shank body 6 and the threaded capture structure 8.

The top end surface 42 of the shank 4 is preferably curved ordome-shaped as shown in the drawings, for contact engagement or positivemating engagement with the rod 21, when the bone screw assembly 1 isassembled, as shown in FIGS. 10 and 11 and in any alignment of the shank4 relative to the head 10. In certain embodiments, the surface 42 issmooth. While not required in accordance with practice of the invention,the surface 42 may be scored or knurled to further increase frictionalpositive mating engagement between the surface 42 and the rod 21.

The shank 4 shown in the drawings is cannulated, having a small centralbore 44 extending an entire length of the shank 4 along the axis A. Thebore 44 is defined by an inner cylindrical wall 45 of the shank 4 andhas a first circular opening 46 at the shank tip 28 and a secondcircular opening 48 at the top surface 42. The bore 44 is coaxial withthe threaded body 6 and the capture structure outer surface 34. The bore44 provides a passage through the shank 4 interior for a length of wire(not shown) inserted into the vertebra 15 prior to the insertion of theshank body 6, the wire providing a guide for insertion of the shank body6 into the vertebra 15.

Referring to FIGS. 1 and 6 through 10, the head 10 has a generallyU-shaped appearance with a partially cylindrical inner profile and afaceted outer profile; however, the outer profile could also bepartially cylindrical. The head 10 includes a somewhat spherical base 50integral with a pair of upstanding arms 52 and 54 forming a U-shapedcradle and defining a U-shaped channel 56 between the arms 52 and 54with an upper opening 57 and a lower seat 58 having substantially thesame radius as the rod 21 for operably snugly receiving the rod 21.

Each of the arms 52 and 54 has an interior surface 60 that defines theinner cylindrical profile and includes a partial helically wound guideand advancement structure 62. In the illustrated embodiment, the guideand advancement structure 62 is a partial helically wound interlockingflange form configured to mate under rotation with a similar structureon the closure top 18, as described more fully below. However, it isforeseen that the guide and advancement structure 62 could alternativelybe a V-shaped thread, a buttress thread, a reverse angle thread or otherthread like or non-thread like helically wound advancement structuresfor operably guiding under rotation and advancing the closure topdownward between the arms 52 and 54.

Tool engaging apertures 64 and 65 are formed within the arms 52 and 54,respectively which may be used for holding the head 10 during assemblywith the shank 4 and the retainer structure 12 and also during theimplantation of the shank body 6 into a vertebra 15.

Communicating with the apertures 64 and 65 are respective upwardlyprojecting, hidden inner recesses 68 and 69. The holding tool (notshown) is sized and shaped to have structure to mate with and to bereceived in the apertures 64 and 65 and locked into place by pulling theholding tool slightly axially upward relative to the base 50 and towardthe upper opening 57 of the channel 56 formed by the arms 52 and 54. Theholding tool and respective apertures 64 and 65 can be configured for aflexible snap on/spring off engagement wherein the holding tool hasflexible legs which splay outwardly to position the tool for engagementin the apertures 64 and 65. It is noted that the apertures 64 and 65 andthe cooperating holding tool may be configured to be of a variety ofsizes and locations along any of the surfaces of the arms 52 and 55, forexample, extending into a face 75 or disposed only at a single face orfacet.

Communicating with and located beneath the U-shaped channel 56 of thehead 10 is a chamber or cavity 78 substantially defined by an innersurface 80 of the base 50, the cavity 78 opens upwardly into theU-shaped channel 56. The inner surface 80 is substantially spherical,with at least a portion thereof forming a partial internal sphericalseating surface 82 having a first radius. The surface 82 is sized andshaped for mating with the retainer structure 12, as described morefully below.

The base 50 further includes a restrictive neck 83, having a secondradius R and defining a bore 84 communicating with the cavity 78 and alower exterior 86 of the base 50. The bore 84 is coaxially aligned withrespect to a rotational axis B of the head 10. The neck 83 andassociated bore 84 are sized and shaped to be smaller (the secondradius) than a radial dimension of the retainer structure 12 (the firstradius), as will be discussed further below, so as to form a restrictionat the location of the neck 83 relative to the retainer structure 12, toprevent the retainer structure 12 from passing from the cavity 78 andout into the lower exterior 86 of the head 10 when the retainerstructure 12 is seated.

The inner surface 80 further defines an elongate upper loading recess 87for accommodating and loading the retainer structure 12 into the cavity78. The loading recess 87 is generally vertically disposed in the head10, extending between and communicating with both the channel 56 and thecavity 78, allowing for ease in top loading the retainer structure 12into the cavity through the upper opening 57 and otherwise allowing forthe spherical wall 80 of the head 10 to have a comparatively enlargedradius to allow for increased thickness and strength of the head base50; however, the loading recess 87 is not always necessary.

The retainer structure or ring 12 is used to retain the capturestructure 8 of the shank 4 within the head 10. The retainer structure12, best illustrated by FIGS. 1-3 and 6-8, has an operational centralaxis that is the same as the elongate axis A associated with the shank4, but when the retainer structure 12 is separated from the shank 4, theaxis of rotation is identified as axis C, as shown in FIG. 3. Theretainer structure 12 has a central bore 90 that passes entirely throughthe retainer structure 12 from a top surface 92 to a bottom surface 94thereof. A first inner cylindrical surface 96 defines a substantialportion of the bore 90, the surface 96 having a helically woundadvancement structure thereon as shown by a helical rib or thread 98extending from adjacent the bottom surface 94 to adjacent a flat,seating surface 99 disposed perpendicular to the inner surface 96.

Although a simple helical rib 98 is shown in the drawings, it isforeseen that other helical structures including other types of threads,such as buttress and reverse angle threads, and non threads, such ashelically wound flanges with interlocking surfaces, may be alternativelyused in an alternative embodiment of the present invention. The innercylindrical surface 96 with helical rib 98 are configured to mate underrotation with the capture structure outer surface 34 and helicaladvancement structure or thread 36, as described more fully below.

The retainer structure 12 further includes a second inner wall orcylindrical surface 102, coaxial with the first inner cylindricalsurface 96. The surface 102 is disposed between the seating surface 99and the top surface 92 of the retainer structure 12 and has a diametergreater than that of the cylindrical surface 96. As will be describedmore fully below, the cylindrical surface 102 in cooperation with theseating surface 99 and the surface 38 of the retainer structure 12,provide a recess about the base of the tool engagement structure 40 anda stable seating surface for the tool 31, as shown in FIG. 9. The wall102 which is the outer wall of the recess may be shaped to fit an outersurface of the tool 31 and may be faceted or especially hexagonal inshape to better grip the tool 31.

The retainer structure or ring 12 has a radially outer partiallyspherically shaped surface 104 sized and shaped to mate with the partialspherical shaped seating surface 82 of the head and having a thirdradius approximately equal to the first radius associated with thesurface 82. The retainer structure third radius is larger than thesecond radius R of the neck 83 of the head 10. Although not required, itis foreseen that the outer partially spherically shaped surface 104 maybe a high friction surface such as a knurled surface or the like.

The elongate rod or longitudinal member 21 that is utilized with theassembly 1 can be any of a variety of implants utilized inreconstructive spinal surgery, but is normally a cylindrical elongatestructure having a cylindrical surface 106 of uniform diameter andhaving a generally smooth surface. The rod 21 is preferably sized andshaped to snugly seat near the bottom of the U-shaped channel 56 of thehead 10 and, during normal operation, is positioned slightly above thebottom of the channel 56 at the lower seat 58. In particular, the rod 21normally directly or abutingly engages the shank top surface 42, asshown in FIG. 10 and is biased against the dome shank top surface 42,consequently biasing the shank 4 downwardly in a direction toward thebase 50 of the head 10 when the assembly 1 is fully assembled. For thisto occur, the shank top surface 42 must extend at least slightly intothe space of the channel 56 when the retainer structure 12 is snuglyseated in the lower part of the head cavity 80. The shank 4 and retainerstructure 12 are thereby locked or held in position relative to the head10 by the rod 21 firmly pushing downward on the shank top surface 42.

With reference to FIGS. 1, 10 and 11, the closure structure or closuretop 18 can be any of a variety of different types of closure structuresfor use in conjunction with the present invention with suitable matingstructure on the upstanding arms 52 and 54. In the embodiment shown, theclosure top 18 is rotatably received between the spaced arms 52 and 54.

The illustrated closure top 18 has a generally cylindrical shaped base108 with an upwardly extending break-off head 110. The base 108 includesa helically wound guide and advancement structure 111 that is sized,shaped and positioned so as to engage and interlock with the guide andadvancement structure 62 on the arms 52 and 54 to provide for rotatingadvancement of the closure structure 18 into the head 10 when rotatedclockwise and, in particular, to cover the top or upwardly open portionof the U-shaped channel 56 to capture the rod 21, preferably withoutsplaying of the arms 52 and 54. The closure structure 18 also operablybiases against the rod 21 by advancement and applies pressure to the rod21 under torquing, so that the rod 21 is urged downwardly against theshank top end surface 42 that extends up into the channel 56. Downwardbiasing of the shank top surface 42 operably produces a frictionalengagement between the rod 21 and surface 42 and also urges the retainerstructure 12 toward the base 50 of the head 10, so as to frictionallyseat the retainer structure external spherical surface 104 fixedlyagainst the partial internal spherical seating surface 82 of the head10, also fixing the shank 4 and retainer structure 12 in a selected,rigid position relative to the head 10.

In the embodiment shown, the closure structure includes a break-off head110 secured to the base 108 at a neck 114 that is sized and shaped so asto break away at a preselected torque that is designed to properly seatthe retainer structure 12 in the head 10. The break-off head 110includes an external faceted surface 115 that is sized and shaped toreceive a conventional mating socket type head of a driving tool (notshown) to rotate and torque the closure structure 18. The break-off head110 also includes a central bore 117 and grooves 118 for operablyreceiving manipulating tools.

The closure structure 18 also includes removal tool engagement structurewhich in the present embodiment is in the form of a hex-shaped andaxially aligned aperture 116 disposed in the base 108, as shown in FIGS.10 and 11. The hex aperture 116 is accessible after the break-off head110 breaks away from the base 108. The aperture 116 is coaxial with thehelically wound guide and advancement structure 111 and is designed toreceive a hex tool, of an Allen wrench type, into the aperture 116 forrotating the closure structure base 108 subsequent to installation so asto provide for removal thereof, if necessary. Although a hex-shapedaperture 116 is shown in the drawings, the tool engagement structure maytake a variety of tool-engaging forms and may include one or moreapertures of various shapes, such as a pair of spaced apart apertures,or a left hand threaded bore, or an easy out engageable step down bore,or a Torx aperture, or a multi-lobular aperture or the like.

Prior to the polyaxial bone screw assembly 1 being placed in useaccording to the invention, the ring-like retainer structure 12 istypically first inserted or top-loaded, into the head U-shaped channel56, as is shown in dotted lines in FIG. 6, and then into the cavity 78through the vertical loading recess 87 to dispose the structure 12within the inner surface 80 of the head 10. Then, the retainer structure12 is rotated approximately 90 degrees so as to be coaxial with the head10 and then seated in sliding engagement with the seating surface 82 ofthe head 10, also shown in FIG. 6.

With reference to FIG. 7, the shank capture structure 8 is then insertedor bottom-loaded into the head 10 through the bore 84 defined by theneck 83. The retainer structure 12, now disposed in the head 10 iscoaxially aligned with the shank capture structure 8 so that the helicaladvancement structure 36 rotatingly mates with the helical advancementstructure 98 of the retainer structure 12.

The shank 4 and or the retainer structure 12 are rotated to fully matethe structures 36 and 98 along the respective cylindrical surfaces 34and 96, as shown in FIG. 7, fixing the capture structure 8 to theretainer structure 12, until the seating surface 38 and the seatingsurface 99 are contiguous and disposed in the same plane and the rim 37abuts the surface 94 of the retainer structure 12 as shown in FIG. 8.Permanent, rigid engagement of the capture structure 8 to the retainerstructure 12 may be further ensured and supported by the use ofadhesive, a spot weld, deforming one or both threads with a punch or thelike.

As shown in FIG. 8, at this time the shank 4 is in slidable androtatable engagement with the head 10, while the capture structure 8 andthe lower aperture or neck 83 of the head 10 cooperate to maintain theshank body 6 in rotational relation with the head 10. According to theembodiment of the invention shown in FIGS. 1-11, only the retainerstructure 12 is in slidable engagement with the head spherical seatingsurface 82. Both the capture structure 12 and threaded portion of theshank body 6 are in spaced relation with the head 10.

It is believed that an advantage to this embodiment is that, althoughthe shank 6 could engage the head lower aperture or neck 83 when rotatedfully relative to the head 10 as best illustrated in FIG. 8, upper shankbody 6 does not contact the lower spherical seating surface 82, so thatrotational stresses between the capture structure 8 and the retainerstructure 12 are lessened, making it less likely that the retainerstructure 12 would loosen from the capture structure 8 or that thecapture structure would fail or break when the assembly 1 is implantedand loaded.

An extent of rotation is shown in FIG. 8 where it is illustrated thatthe shank body 6 can be rotated through a substantial angular rotationrelative to the head 10, both from side to side and from front to rearso as to substantially provide a universal or ball joint wherein theangle of rotation is only restricted by engagement of the neck 26 of theshank body 6 with the neck or lower aperture 83 of the head 10.

With reference to FIG. 9, the assembly 1 is then typically screwed intoa bone, such as the vertebra 15, by rotation of the shank 4 using thedriving tool 31 that operably drives and rotates the shank 4 byengagement thereof with the hexagonally shaped extension head 40 of theshank 4. Preferably, when the driving tool 31 engages the head 40, anend portion 118 thereof is disposed in a recess defined by the head 40,the seating surface 38, the contiguous seating surface 99 and the innercylindrical surface 102, with a bottom surface 119 of the tool 31contacting and frictionally engaging both the seating surface 38 and theseating surface 99. Some frictional engagement between an outer surface120 of the tool 31 with the cylindrical surface 102 may also beachievable during rotation of the driving tool 31.

It is foreseen that in other embodiments according to the invention, thetool engaging recess may be defined by only one of the seating surface38 or the seating surface 99. For example, a retainer structure mightnot include a seating surface, so a driving tool might seat or mate onlywith a seating surface or an internal aperture of a shank capturestructure. Alternatively, the tool engaging end of a capture structuremight be of a size and shape that a driving tool substantially seats ona seating surface of a retainer structure or ring and not the capturestructure.

Typically, the head 10 and the retainer structure 12 are assembled onthe shank 4 before inserting the shank body 6 into the vertebra 15, butin certain circumstances, the shank body 6 can be first partiallyimplanted in the bone with the capture structure 8 extending proud toallow assembly with the head 10 utilizing the retainer structure 12.Then the shank body 6 can be further driven into the vertebra 15.

With reference to FIGS. 1 and 5 as well as FIG. 9, the vertebra 15 maybe pre-drilled to minimize stressing the bone and have a guide wire (notshown) that is shaped for the cannula 44 inserted to provide a guide forthe placement and angle of the shank 4 with respect to the vertebra 15.A further tap hole may be made using a tap with the guide wire as aguide. Then, the assembly 1 or the solitary shank 4, is threaded ontothe guide wire utilizing the cannulation bore 44 by first threading thewire into the bottom opening 46 and then out of the top opening 48. Theshank 4 is then driven into the vertebra 15, using the wire as aplacement guide.

With reference to FIGS. 1, 10 and 11, the rod 21 is eventuallypositioned within the head U-shaped channel 56, and the closurestructure or top 18 is then inserted into and advanced between the arms52 and 54 so as to bias or push against the rod 21. The break-off head110 of the closure structure 18 is twisted to a preselected torque, forexample 90 to 120 inch pounds, to urge the rod 21 downwardly. The shanktop end surface 42, because it is rounded to approximately equallyextend upward into the channel 56 approximately the same amount nomatter what degree of rotation exists between the shank 4 and head 10and because the surface 42 is sized to extend upwardly into the U-shapedchannel 56, the surface 42 is engaged by the rod 21 and pusheddownwardly toward the base 50 of the head 10 when the closure structure18 biases downwardly toward and onto the rod 21. The downward pressureon the shank 4 in turn urges the retainer structure 12 downward towardthe head seating surface 82, with the retainer structure seating surface99 in frictional engagement with the head seating surface 82. As theclosure structure 18 presses against the rod 21, the rod 21 pressesagainst the shank and the retainer structure 12 that is now rigidlyattached to the shank 4 which in turn becomes frictionally and rigidlyattached to the head 10, fixing the shank body 6 in a desired angularconfiguration with respect to the head 10 and rod 21.

FIG. 10 illustrates the polyaxial bone screw assembly 1 and includingthe rod 21 and the closure structure 18 positioned in a vertebra 15. Theaxis A of the bone shank 4 is illustrated as not being coaxial with theaxis B of the head 10 and the shank 4 is fixed in this angular lockedconfiguration. Other angular configurations can be achieved, as requiredduring installation surgery due to positioning of the rod 21 or thelike.

If removal of the assembly 1 and associated rod 21 and closure structure18 is necessary, disassembly is accomplished by using a driving tool ofan Allen wrench type (not shown) mating with the aperture 116 and turnedcounterclockwise to rotate the base 108 and reverse the advancementthereof in the head 10. Then, disassembly of the assembly 1 isaccomplished in reverse order to the procedure described previouslyherein for assembly.

With reference to FIGS. 12-25, the reference number 201 generallyrepresents a second or alternative embodiment of a polyaxial bone screwapparatus or assembly according to the present invention. As shown inFIG. 12, the assembly 201 includes a shank 204 that has a body 206integral with a capture structure 208, a head 210, and a retainerstructure 212. The shank 204, head 210 and retainer structure 212 aretypically assembled prior to implantation of the shank body 206 into avertebra 215, as shown in FIGS. 18-22.

FIG. 23 further shows a closure assembly 218 of the invention forbiasing a longitudinal member such as a rod 221 against the capturestructure 208 so as to fix the rod 221 relative to the vertebra 215.

Similar to the embodiment shown in FIGS. 1-11, the alternativeembodiment of the invention 201 provides for the head 210 and shank 204to cooperate in such a manner that the head 210 and shank 204 can besecured at any of a plurality of obtuse angles, relative to one anotherand within a selected range of angles both side to side and front torear, to enable flexible engagement of the assembly 201 with the rod221, as shown in FIG. 19, and will be described in more detail below.That is the two elements, the head 210 and the shank 204, arearticulatable or rotatable relative to each other within a preselectedrange of movement until locked in a fixed configuration at the end ofthe procedure.

The shank 204, best illustrated in FIGS. 12 and 16 is elongate, with theshank body 206 having a helically wound bone implantable thread 224extending from near a neck 226 located adjacent to the capture structure208 to a tip 228 of the body 206 and extending radially outwardtherefrom. During use, the body 206 utilizing the thread 224 isimplanted into the vertebra 215 leading with the tip 228 and driven downinto the bone with an installation tool 231 to adjacent the neck 226 asshown in FIG. 22, described more fully in the paragraphs below. Theshank 204 has an elongate axis of rotation generally identified by thereference letter A′.

The neck 226 extends axially outward and upward from the shank body 206.The neck 226 constricts to a reduced radius as compared to an adjacenttop 232 of the body 206. Further extending axially and outwardly fromthe neck 226 is the capture structure 208 that provides a connective orcapture apparatus disposed at a distance from the shank body top 232 andthus at a distance from the vertebra 215 when the body 206 is implantedin the vertebra 215. The capture structure 208 is configured forconnecting the shank 204 with the head 210 and the retainer structure212.

The capture structure 208 includes an outer substantially cylindricalsurface 234 contiguous to the neck 226 and coaxial with the shank body206. The cylindrical surface 234 is also contiguous and disposedsubstantially perpendicular to a seating surface 236. The seatingsurface 236 is also coaxial with the shank body 206 and the cylindricalsurface 234. Both the cylindrical surface 234 and the seating surface236 are configured to come into frictional engagement with the retainerstructure 212, as described more fully below.

Perpendicular to and contiguous with the seating surface 236 is a secondcylindrical surface 238 having a helically wound advancement structurethereon as shown by a helical rib or thread 240 extending from adjacentthe seating surface 236 to adjacent a rod engagement dome 242. Althougha simple helical rib 240 is shown in the drawings, it is foreseen thatother helical structures including other types of threads, such asbuttress and reverse angle threads, and non threads, such as helicallywound flanges with interlocking surfaces, may be alternatively used inan alternative embodiment of the present invention.

The top end surface or dome 242 of the shank 204 is preferably convex,domed or curved as shown in the drawings, and sized and positioned forpositive engagement with the rod 221 when the bone screw assembly 201 isassembled, as shown in FIGS. 24 and 25. If desired, the dome 242 may bescored or knurled. In certain embodiments, the purpose of the dome 242is simply to be engaged by the rod 221 during assembly and be biaseddownwardly in such a manner as to frictionally engage the retainerstructure 212, which is secured to the shank 206 at this time, withinthe head 210, as described below. The dome 242 may be radiused so thatthe dome 242 engages the rod 221 at generally the same level or heightrelative to the head channel lower surface 258, even as the head 210 isswivelled relative to the shank 204. However in other embodiments thedome 242 can have other shapes.

In the embodiment shown in FIGS. 12-25, the shank body 206 and capturestructure 208 components are integral. Furthermore the shank 204 iscannulated, having a small cylindrical central bore 244 extending anentire length of the shank 204 along the axis A′. The bore 244 isdefined by an inner cylindrical wall 245 of the shank 204 and has afirst circular opening 246 at the shank tip 228 and a second circularopening 248 at the dome top surface 242. The bore 244 is coaxial withthe threaded body 206 and capture structure outer cylindrical surfaces234 and 238. The bore 244 provides a passage through the shank 204interior for a length of wire (not shown) inserted into the vertebra 215prior to the insertion of the shank body 206, the wire providing a guidefor accurate insertion of the shank body 206 into the vertebra 215.

Referring to FIGS. 12, 17 and 18, the head 210 is substantiallycylindrical in external profile and includes a base portion 250 integralwith a pair of upstanding arms 252 and 254 forming a U-shaped channel256 between the arms 252 and 254 with an upper opening 257 and the lowersurface 258 having substantially the same radius as the rod 221. Inoperation, the rod 221 preferably is located just above the channellower surface 258.

Each of the arms 252 and 254 has an interior surface 260 that defines aninner cylindrical profile and includes a partial helically wound guideand advancement structure 262. Similar to the guide and advancementstructure 62 shown with respect to FIGS. 1-11, the guide and advancementstructure 262 is a partial helically wound flange form configured tomate and interlock under rotation about an axis B′ with a similarstructure disposed on the closure top assembly 218, as described morefully below. However, it is foreseen that the guide and advancementstructure 262 could alternatively be a V-shaped thread, a buttressthread, a reverse angle thread or other thread like or non-thread likehelically wound advancement structures for operably guiding underrotation and advancing the closure top between the arms 252 and 254.Also, it is foreseen that this mating advancement structure could belocated on the cylindrical external surfaces of the arms 252 and 254.

The head 210 includes external, closed end grip bores 264 and 265disposed on the respective arms 252 and 254 for positive engagement by aholding tool (not shown)to facilitate secure gripping of the head 210during assembly of the head 210 with the shank 204 and retainerstructure 212. Furthermore, the grip bores 264 and 265 may be utilizedto hold the head 210 during the implantation of the shank body 206 intothe vertebra 215. The bores 264 and 265 are centrally located on therespective arms 252 and 254. However, it is noted that the bores 264 and265 may be configured to be of a variety of sizes and locations alongouter surfaces of the arms 252 and 254.

Communicating with the U-shaped channel 256 of the head 210 is a chamberor cavity 268 substantially defined by an inner surface 270 of the base50, the cavity 268 opening upwardly into the U-shaped channel 256. Theinner surface 270 is substantially spherical, with at least a portionthereof forming a partial internal spherical seating surface 272 havinga first radius, the surface 272 for mating with the retainer structure212, as described more fully below.

The base 250 further includes a restrictive aperture, opening or neck274, having a second radius R′ and partially defining a bore 276communicating with the cavity 268 and a bottom exterior 278 of the base50. The bore 276 is coaxial with a rotational axis B′ of the head 210. Abevel 280 extends between the neck 274 and the bottom exterior 278. Theneck 274 and associated bore 276 are sized and shaped to be smaller thana radial dimension of the retainer structure 212, as will be discussedfurther below, so as to form a restriction at the location of the neck274 relative to the retainer structure 212, to prevent the structure 212from passing between the cavity 268 and the bottom exterior 278 of thehead 210, when fully seated. The bevel 280 widens the angular range ofthe shank 204 when assembled with the head 210.

The retainer structure or ring 212 is used to retain the capturestructure 208 of the shank 204 within the head 210. The retainerstructure 212, best illustrated by FIGS. 12-14, has an operationalcentral axis that is the same as the elongate axis A′ associated withthe shank 204, but when the retainer structure 212 is separated from theshank 204, the axis of rotation is identified as axis C′, as shown inFIG. 14. The retainer structure 212 has a central bore 282 that passesentirely through the retainer structure 212 from a top surface 284 to abottom surface 285 thereof. A first inner cylindrical surface 286defines a substantial portion of the bore 282, the surface 286 having ahelically wound advancement structure thereon as shown by a helical ribor thread 288 extending from adjacent the top surface 284 to adjacent aseating surface 290 disposed perpendicular to the inner surface 286.

Although a simple helical rib 288 is shown in the drawings, it isforeseen that other helical structures including other types of threads,such as buttress and reverse angle threads, and non threads, such ashelically wound flanges with interlocking surfaces, may be alternativelyused in an alternative embodiment of the present embodiment. The firstinner cylindrical surface 286 with helical rib 288 are configured tomate under rotation with the capture structure outer surface 238 andhelical advancement structure or thread 240, as described more fullybelow.

The retainer structure 212 further includes a second inner cylindricalsurface 292, coaxial with the first inner cylindrical surface 286. Thesurface 292 is disposed between the seating surface 290 and the bottomsurface 285 of the retainer structure 212 and has a diameter greaterthan that of the cylindrical surface 286. As will be described morefully below, the cylindrical surface 292 in cooperation with the seatingsurface 290, provide a recess for insertion of the shank 204 thereintoand the seating surface 290 provides a frictional contact or seatingsurface for the seating surface 236 of the capture structure 108 asshown in FIGS. 18 and 19.

The retainer structure or ring 212 has a radially outer partiallyspherically shaped surface 294 sized and shaped to mate with the partialspherical shaped seating surface 272 of the head and having a thirdradius approximately equal to the first radius associated with thesurface 272. The retainer structure third radius is larger than thesecond radius R′ of the restrictive neck 274 of the head 210.

The retainer structure 212 shown in FIG. 13 further includes atransverse slot 296 formed in the top surface 284 thereof for engagementof the driving tool 231 shown in FIG. 22. It is foreseen that a retainerstructure according to the present invention may include two or moreslots in the retainer top surface, or other types of apertures forengaging with a cooperating driving tool. The slot 296 is defined by apair of spaced, parallel walls 298 perpendicular to a base 300. The slot296 extends out to the outer spherical surface 294 from each side of thecentral bore 282. A plane aligned with the center of the slot 296intersects the rotational axis C′. The tool 231 includes a pair ofspaced slot engaging extensions 302 sized and shaped to seat in the slot296 on either side of the central bore 282 and with the regiontherebetween configured to clear the rod-engagement dome 242 duringassembly and while driving and rotating the shank body 206 into thevertebra 215.

With reference to FIGS. 20 and 21, the slot 296 is preferably sized suchthat, after the shank 204, head 210 and retainer structure 12 have beenassembled, a tool such as the illustrated punch 304 may be inserted intothe slot 296 to deform the helical rib 240 of the capture structure 208by causing a nick or deformity 305 thereon, thereby preventing relativerotation therebetween and rigidly fixing the rib 240 against the helicalrib 288 of the retainer structure 212, ensuring a fixed relation betweenthe shank capture structure 208 and the retainer structure 212.

The elongate rod or longitudinal member 221 that is utilized with theassembly 201 can be any of a variety of implants utilized inreconstructive spinal surgery, but is normally a cylindrical elongatestructure having a cylindrical surface 306 of uniform diameter. The rod221 is preferably sized and shaped to snugly seat at the lower channelseat 258 near the bottom of the U-shaped channel 256 of the head 210,and, during normal operation, is positioned slightly above the bottom ofthe channel 256. In particular, the rod 221 normally engages the shanktop surface or dome 242, as shown in FIG. 24 and is biased against thedome 242, consequently biasing the shank 204 downwardly in a directiontoward the base 250 of the head 210 when the assembly 201 is fullyassembled.

With reference to FIGS. 23-25, the closure or top assembly 218 can beany of a variety of different types of closure structures for use inconjunction with the present invention with suitable mating structureinternally or externally on the upstanding arms 252 and 254. Theillustrated closure top assembly 218 includes a cylindrical closure plug310 and a cylindrical inner set screw or plug 312. The inner plug 312includes a pointed rod engaging projection or point 314 at a bottomsurface thereof and a tool engagement aperture 315 disposed in anopposite or top surface thereof, illustrated in FIGS. 24 and 25 as a hexaperture. However, the tool engagement structure 315 may take a varietyof tool-engaging forms and may include more than one aperture, such as apair of spaced apertures or other shapes such as Torx or the like.

The closure plug 310 includes an outer helically wound guide andadvancement structure 316 that is sized, shaped and positioned so as toengage the guide and advancement structure 262 on the arms 252 and 254to provide for the rotation of the closure plug 310 into the head 210and, in particular, to enclose the top of the U-shaped channel 56 tocapture the rod 221, preferably without splaying of the arms 252 and254. The closure plug 310 is a hollow cylinder and also includes aninner threaded cylindrical wall 317 sized and shaped to receive androtatingly mate with an outer threaded surface 318 of the inner plug orset screw 312. As shown in FIG. 25, the closure plug 310 furtherincludes a pair of transverse slots 319 in perpendicular relation, theslots 319 for engagement with a driving tool (not shown). The hexaperture 315, closure plug inner wall 317, inner plug wall 318, and arms252 and 254 are configured so as to be coaxial upon assembly. A hexdriving tool 320 can be inserted into the aperture 315 of the inner plug312 to drive and rotate both the inner plug 312 into the closure plug310 and the closure plug 310 into the head arms 252 and 254. Preferably,the closure plug 310 is first driven and rotated into the arms 252 and254 by engaging a tool with the slots 319, followed by the inner plug312 being rotated individually into the closure plug 312 by engagementwith the tool 320.

The closure assembly 218 operably biases against the rod 221, with theprojection 314 frictionally engaging and abrading the rod surface 306and thereby applying pressure to the rod 221 under torquing, so that therod 221 is urged downwardly against the rod-engagement dome 242.Downward biasing of the dome 242 operably produces a frictionalengagement between the rod 221 and the dome 242 and also urges theretainer structure 212 toward the base 250 of the head 210, so as tofrictionally seat the retainer structure external spherical surface 294fixedly or in a locked configuration against the partial internalspherical seating surface 272 of the head 210, also fixing the shank 204and retainer structure 212 in a selected, rigid angular positionrelative to the head 210.

If necessary, the hex tool 320 may be used to loosen the assemblysubsequent to installation, and for removal of the plugs 310 and 312.

When the polyaxial bone screw assembly 201 is placed in use according tothe invention, the closed ring-like retainer structure 212 is typicallyfirst inserted or top-loaded, into the head U-shaped channel 256 andthen into the cavity 268 within the inner surface 270 of the head 210.Although not shown, the inner surface 270 may include a loading recesssimilar to the recess 87 disclosed with respect to the first embodimentassembly 1, and may be loaded into the head 210 in similar fashion. Theretainer structure 212 is then seated with the surface 294 in slidingengagement with the spherical seating surface 272 of the head 210, asshown in FIG. 17. Although not required, both the retainer structure andhead surfaces 294 and 272, respectively maybe high friction surfaces,such as knurled surfaces, or the like.

With reference to FIGS. 17 and 18, the shank capture structure 208 isinserted or bottom-loaded into the head 210 through the bore 276 definedby the neck 274. The retainer structure 212, now disposed in the head210 is coaxially aligned with the shank capture structure 208 so thatthe helical advancement structure 240 of the capture structure 208rotatingly mates with the helical advancement structure 288 of theretainer structure 212. The shank 204 and or the retainer structure 212are rotated to fully mate the structures 240 and 288 along therespective cylindrical surfaces 238 and 286, as shown in FIG. 18,securing or fixing the capture structure 208 to the retainer structure212, until the seating surface 236 and the seating surface 290 are infrictional contact, as shown in FIG. 19.

With reference to FIGS. 20 and 21, permanent, fixed or rigid engagementof the capture structure 208 to the retainer structure 212 may befurther enhanced by deforming the helical advancement structure orthread 240 by inserting the pointed tool 304 into the slot 296 andmarring or nicking the helical rib 240 with the tool 304, resulting inthe nick or deformity 305, as is shown in FIG. 21. The deformity 305causes the rib 240 to abut against the helical rib 288 of the retainerstructure 212, thereby resisting unscrewing and ensuring a fixedrelation between the shank capture structure 208 and the retainerstructure 212. As with the assembly 1, the fixed relation between therib 240 and the rib 288 may also be accomplished by the use of anadhesive, or spot weld or the like, in any area of the retainerstructure cylindrical surface 238, especially where exposed by the slot296.

As shown in FIG. 19, the shank 204 with integral capture structure 208and attached retainer structure 212 are in pivotable engagement with thehead 210. The capture structure 208 and the neck 274 of the head 210,connecting the shank 204 to the head 210 and after locking the retainerstructure 212 keeping the shank body 206 in fixed rotational relationwith the head 210.

According to the embodiment of the invention shown in FIGS. 12-25, onlythe retainer structure 212 is in slidable engagement with the headspherical seating surface 272. The capture structure 208 and threadedportion of the shank body 206 are in spaced relation with the head 210,although the shank outer neck 226 could engage the head restrictive neck274 at a full rotation, as best illustrated in FIG. 24.

An extent of rotation is shown in FIG. 19 in phantom lines where it isillustrated that the shank body 206 can be rotated through a substantialangular rotation relative to the head 210, both from side to side andfrom front to rear so as to substantially provide a universal or balljoint wherein the angle of rotation is only restricted by engagement ofthe neck 226 of the shank body 206 with the neck 274 of the head 210.

With reference to FIG. 22, the assembly 201 is then typically screwedinto a bone, such as the vertebra 215, by rotation of the shank 204using the driving tool 231 that operably drives and rotates the shank204 by engagement thereof with the transverse slot 296 of the retainerstructure 212. Preferably, when the driving tool 231 engages theretainer structure 212, each of the tool prong like extensions 302 aredisposed in a recess defined by the slot walls 298 and the base of theslot 300, with the tool extensions 302 seated upon and driving againstthe slot base 300.

The head 210 and the retainer structure 212 are assembled on the shank204 before inserting the shank body 206 into the vertebra 215. Withreference to FIG. 16 and FIG. 22, the vertebra 215 may be pre-drilled tominimize stressing the bone, as well as the connection between theretainer ring and capture structure, and a guide wire inserted toprovide a guide for the placement and angle of the shank 204 withrespect to the vertebra 215 (not shown). A bone screw shaped tap holemay be made utilizing a tap. Then, the assembly 201 or the solitaryshank 204, is threaded onto the guide wire utilizing the cannulationbore 244 by first threading the wire into the bottom opening 246 andthen out of the top opening 248. The shank 204 is then driven into thevertebra 215, using the wire as a screw placement guide and the wire isthen removed.

With reference to FIGS. 23-25, the rod 221 is eventually positionedwithin the head U-shaped channel 256, and the closure assembly 218 isthen inserted into and advanced between the arms 252 and 254 so as tobias or push against the rod 221. Specifically, a driving tool (notshown, but could be the same tool 231 shown in FIG. 22) is inserted intothe slots 319 of the closure plug 310 to drive and rotate the closureplug 310 into the head arms 252 and 254. Subsequently, the hex drivingtool 320 is inserted into the aperture 315 of the inner plug 312 todrive and rotate the inner plug 312 into the closure plug 310.

The shank top end surface or dome 242, because it is rounded and sizedto extend upwardly into the U-shaped channel 256, is engaged by the rod221 and pushed downwardly toward the base 250 of the head 210 when theouter closure structure and inner plug projection 314 bias downwardlytoward and onto the rod 221. The downward pressure on the shank 204 inturn urges the retainer structure 212 downward toward the head seatingsurface 272, with the retainer structure seating surface 294 intofrictional engagement with the head seating surface 272. As the outerplug and inner set screw 312 press against the rod 221, the rod 221presses against the shank and rigidly attached retainer structure 212,which in turn becomes rigidly and frictionally attached to the head 210,fixing the shank body 206 in a desired angle with respect to the head210 and rod 221.

FIGS. 24 and 25 illustrate the polyaxial bone screw assembly 201, therod 221 and the closure assembly 218 positioned in the vertebra 215. Theaxis A′ of the bone shank 204 is illustrated as not being coaxial withthe axis B′ of the head 210 and the shank 204 is fixed in this angularlocked configuration. Other angular configurations can be achieved, asrequired during installation surgery due to positioning of the rod 221or the like.

If removal of the assembly 201 and associated rod 221 and closureassembly 218 is necessary, disassembly is accomplished by using thedriving tool 320 mating with the aperture 315 to rotate the inner plugor set screw 312 and reverse the advancement thereof in the outerclosure plug 310. Subsequently, the outer plug 310 is loosened by matingthe slots 319 with a driver (not shown) to reverse the advancement ofthe plug 310 in the arms 252 and 254. It may be possible to loosen boththe inner plug 312 and the closure plug 310 with the tool 320, thusloosening the closure plug 310 from the head arms 252 and 254, as theouter plug 310 and inner plug 312 may be joined together by threads atthe lower ends thereof becoming deformed by engagement with the rod 221.Then, disassembly of the assembly 1 is accomplished in reverse order tothe procedure described previously herein for assembly. For disassembly,it is preferred that the retaining structure 312 be strongly secured tothe shank 310 by deformation of the threads 238 and 288 or by otherlocking structure such as welding or pins so that both are assured ofbeing removed as a single unit.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A pivotal bone anchor multi-part assembly for surgicalimplantation, the multi-part assembly including: a shank and a headhaving a pair of upstanding arms, each with a top surface and anexterior surface adjacent the top surface, the arms forming a channelfor receiving a rod, the arms having an internal surface with adiscontinuous helically wound guide and advancement structure; a unitaryclosure for closing the channel and locking the rod between the arms;and a two-part closure for closing the channel and locking the rodbetween the arms; the two-part closure comprising: a) an outer plug bodyconfigured as a closed ring with a generally cylindrical shaped externalsurface having a continuous helically wound guide and advancementstructure portion formed thereon, the outer plug body including athreaded central bore extending from a top surface to a bottom surfaceof the outer plug body, at least a portion of the threaded central borebeing circumferentially closed, the outer plug body including anon-threaded drive structure formed in an upper portion of the outerplug body, the drive structure intersecting the threaded central bore;b) an inner plug having a longitudinal axis and an outer surface that isconfigured to be threadedly received in the threaded central bore of theouter plug body, the inner plug having a lower portion that has a solidcross section with a bottom surface that is substantially flat to engageand lock the rod after positioning the rod within the channel, and theinner plug including a drive structure having a non-threaded internalaperture with parallel opposed sides, the non-threaded internal apertureextending from a top surface of the inner plug to a lower tool abutmentsurface, the lower tool abutment surface located substantially nearerthe bottom surface of the inner plug than the top surface; wherein whenthe unitary closure or the two-part closure locks the rod between thearms, no part of the multi-part assembly is positioned over the topsurface or outside of the exterior surface on each upstanding arm; andwherein the unitary closure and the two-part closure are interchangeablefor closing the channel and locking the rod between the arms.
 2. Theassembly according to claim 1, wherein the inner plug is configured tobe threadedly receivable in the outer plug body prior to the two-partclosure being received in the channel formed between the upstanding armsof the head.
 3. The assembly according to claim 1, wherein the bottomsurface of the inner plug comprises a central point.
 4. The assemblyaccording to claim 1, wherein the top surface of the inner plug is flat.5. The assembly according to claim 1, wherein a thread on the outersurface of the inner plug is continuous from the inner plug top surfaceto the bottom surface.
 6. The assembly according to claim 1, wherein theouter plug body drive structure includes a first radially located slotformed in the top surface which extends from the external surface to thethreaded central bore and intersects the threaded central bore of theouter plug body.
 7. The assembly according to claim 6, wherein the outerplug body drive structure includes a second radially located slot formedin the top surface diametrically opposed to the first slot which extendsfrom the external surface to the threaded central bore and intersectsthe threaded central bore.
 8. The assembly according to claim 1, whereinthe internal aperture configured as the inner plug drive structure has across-section with multiple drive surfaces aligned axially about thelongitudinal axis of the inner plug.
 9. The assembly according to claim1, wherein the unitary closure includes a tool-engaging multi-lobularcentral aperture for surgical implantation.